1. Field of the Invention
The present invention relates generally to sources of renewable energy, and more particularly to a submersible turbine-generator unit for ocean and tidal currents.
2. Related Art
Ocean and tidal currents are capable of providing a virtually inexhaustible supply of emission-free renewable energy. Since ocean and tidal currents exist everywhere in the world and are either constantly flowing or extremely predictable, converting the energy in these currents to electricity could provide a predictable, reliable and, in some cases, base load supply of electricity to the electric power systems or remote sites in many parts of the world. Seventy percent (70%) of the world's population lives within 200 miles of an ocean. Accordingly, ocean current energy could become a vital part of the world's energy future.
The tremendous growth in renewable energy over the past several years is well documented and the rate of growth continues to increase each year. With worldwide awareness of the negative environmental impacts of fossil fuels on our global environment, growth in the use of renewable energy appears to be constrained only by the ability to produce and deliver it at an economic price. Wind power, for example, once considered a fringe energy technology, has now entered the mainstream and has been the fastest growing segment of the energy industry over the last several years. Congress' 2005 Energy Bill is the first major piece of U.S. legislation to recognize the vast potential of the waves and currents for deriving clean, renewable energy from our oceans. This pivotal legislation includes many incentives that are expected to accelerate the development and commercialization of technologies to produce electric power from the oceans. This bill also authorized funding of $632 million in fiscal year 2007, $734 million in fiscal year 2008 and $852 million in fiscal year 2009 for renewable energy research, development, demonstration and commercial application projects, including ocean energy projects. These, and other incentives, bode well for the continued development of ocean energy technologies, and the commercialization of ocean energy projects at an increasing pace.
While wind generation is rapidly expanding and is an important piece of solving the world's energy needs, wind resources are limited, power generated by wind is not predictable and “view shed” and “not-in-my-back-yard” issues restrict development of wind projects. In fact, view shed issues have become a major obstacle for develop of most projects, regardless of their societal benefits.
Ocean power generation, on the other hand, has essentially unlimited development potential, is predictable, if not constant. Although power generated from ocean energy can be directly “plugged into” coastal load centers and remote communities, it is not restricted to these markets. A system for marketing renewable energy in the United States and Canada now exists called “Green Tag”. This market system allows a power producer to generate renewable energy in one location and sell it anywhere in the country to satisfy local renewable portfolio standards that have been mandated by various states. Other large markets for ocean derived power include the Federal Power Administrations, such as the Western Area Power Administration, and the United States military, which is under a mandate to increase purchases of renewable energy as an energy independence and national security strategy.
Internationally, the market for renewable energy is virtually unlimited. In European Union countries, for example, a considerable premium over fossil fuel generation is currently being paid for “green” power. There are many potential sites for ocean current energy in Northern Europe near the United Kingdom, in Southern Europe near the mouth of the Mediterranean Sea, as well as off the coasts of South America, Africa and Japan, and many of these countries are providing special incentives to ocean renewable energy projects. In addition, there are countless numbers of island communities where ocean currents accelerate around and between land masses. Coastal communities throughout the world will be the primary beneficiaries of ocean power due to the presence of strong ocean and tidal currents and insufficient energy supply. With its vast and geographically dispersed resources as shown in FIG. 1, ocean current energy has the potential of becoming the next “wind” of renewable energy.
One of the greatest potential sources of ocean current energy in the world is the Florida Current as shown in FIG. 2. The Florida Current is the portion of the Gulf Stream that runs in a northerly direction off the east coast of the United States from the Florida Keys to Cape Hatteras in North Carolina. The Florida Current is a particularly attractive renewable energy resource because it is relatively close to the Florida coast (i.e., generally between 10 and 25 miles) and it flows constantly in a northerly direction at a rate of up to 5 knots.
Although the speed and exact location of the Florida Current can fluctuate from season to season and year to year, it is relatively stable, predictable and wide enough that the center portion is always within the current boundaries. Importantly, it always flows in a northerly direction, twenty-four hours a day, so it provides a continuous, reliable source of energy. The Florida Current alone has the energy potential to produce tens of thousands of megawatts (MW) of electricity. This is enough electricity to power a substantial portion of the households near the southeast coast of the United States.
Since the Florida Current is relatively close to the shore and to the large population centers on the east coast of Florida, where significant and growing demands for electricity exist, it is ideal for development of ocean current power generation. Additionally, the maximum velocities of the Florida Current occur during the peak months of electricity usage during the summer which means the maximum output of the submersible turbine-generator modules of the present invention would occur during periods when the power is most needed.
Recent studies of the current flows in an area of the preferred site within the Florida Current are promising. At 50 meters below the surface, for example, the water velocity distribution was found to be Gaussian. Flows are very consistent—in the range of 0.642 to 2.435 meters per second (1.25 to 4.73 knots) 99.7% of the time (within three standard deviations of the mean). Moreover, the flow direction varies only 1.5 degrees from an otherwise steady northerly direction of flow. At 50 meters below the water surface, the mean velocity is 1.54 meters per second (3.0 knots) with a standard deviation of 0.2988.
The greatest potential for development of tidal current projects in the United States is in Alaska, where tidal flows are greater than anywhere else in the United States. For example, tides in Anchorage within the upper Cook Inlet of Alaska exceed thirty (30) feet and tidal current flows can exceed 8 knots. While Alaska has been an energy rich state with only 626,000 residents and 2,500 MW of electricity generating capacity, most of the state is now paying substantially higher energy rates than those in the “lower 48.” The reasons for this reversal in energy fortunes is that the low cost natural gas in the Anchorage area is rapidly being depleted and there is little or no infrastructure to get the remote energy resources to the areas where it is needed the most. In many areas, electricity is produced by old and inefficient diesel generating plants that are prohibitively expensive and must be subsidized by the state. In reasonably populated areas, the average electric supply rate is approximately $0.12 to $0.15 per kilowatt-hour (kWH) and in rural areas, the rate can reach $0.75 per kWH or more. Due to the severe terrain, weather and environmental constraints in Alaska, there is no integrated transmission system, which has resulted in the proliferation of nearly 120 public and municipal owned utilities.
For the above reasons, the upper Cook Inlet of Alaska can be a primary target for the development of tidal current projects. In addition to providing much needed electricity to the Anchorage area, where approximately one-half of the state's population lives, tidal current generators can be located in tidal currents near to shore in remote, local “pockets” of demand.
As shown in FIG. 3A, two potential tidal generation project sites may be located near the City of Anchorage. Each of the sites has the potential for development of a project with a generating capacity of from 50 to over 100 MW of electricity. Because of the unique submersible feature of tidal current generators according to embodiments of the present invention, the ice which forms on the surface of the Cook Inlet in the winter will not affect either of the sites. The project adjacent to Fire Island could also be developed in conjunction with a wind generation project being developed and installed on Fire Island by Cook Inlet Region and Chugach Electric Company, the local electric utility serving the Anchorage area. Both projects could be easily interconnected with the local utility grid which serves the Anchorage area. Similar sites of equally good potential off the coast of northern Maine are also shown in FIG. 3B.
Using the technology developed herein, off-shore ocean currents could also be used for the production, storage and shipment of hydrogen and/or potable water from sea water from off-shore production facilities. With the abundance of sea water and availability of low cost electricity, as well as the viability of off-shore platform operations as demonstrated in the off-shore oil industry, hydrogen and/or potable water could be produced, stored and shipped in tankers to markets around the world.
Submersible turbine-generator units according to the present invention utilize recent technological advances from several industries and incorporate them into an integrated power system. The industries which have provided these technological advances include the off-shore oil and gas, wind power generation, maritime, shipping and telecommunications. These technological advances include not only unique designs and equipment but also state of the art advanced materials, including composite materials. Such submersible turbine-generator units according to the present invention preferably utilize a highly efficient turbine, known as the advanced design cross-flow turbine (“ADCF Turbine”), which is a derivation of the Darrieus turbine. The efficacy of the ADCF Turbine was demonstrated in a pilot scale project in the summer of 2007 in the United States. The aerodynamic blades of the ADCF Turbine convert the energy in the ocean and tidal currents into mechanical energy that transfers through the turbine shafts to a permanent magnet generator. The generator converts the mechanical energy (i.e., RPM and torque) into electricity. A power electronics system controls, conditions and synchronizes the generated electricity. The synchronized electricity then transmits to on-shore substations via an undersea transmission cable.
Further details regarding ADCF Turbines may be found in the following U.S. Pat. No. 6,293,835 for a “System For Providing Wind Propulsion Of A Marine Vessel Using A Helical Turbine Assembly”; U.S. Pat. No. 6,253,700 for a “Method For Maintaining Flotation Using A Helical Turbine Assembly”, U.S. Pat. No. 6,155,892 for a “Helical Turbine Assembly Operable Under Multidirectional Gas And Water Flow For Power And Propulsion Systems”, U.S. Pat. No. 6,036,443 for a “Helical Turbine Assembly Operable Under Multidirectional Gas And Water Flow For Power And Propulsion Systems”. U.S. Pat. No. 5,642,984 for a “Helical Turbine Assembly Operable Under Multidirectional Fluid Flow For Power And Propulsion Systems”. U.S. Pat. No. 5,577,882 for a “Unidirectional Reaction Turbine Operable Under Reversible Fluid Flow”. U.S. Pat. No. 5,451,138 for a “Unidirectional Reaction Turbine Operable Under Reversible Fluid From Flow”, U.S. Pat. No. 5,451,137 for a “Unidirectional Helical Reaction Turbine Operable Under Reversible Fluid Flow For Power Systems”, the contents of each of which is incorporated herein by reference.